Pumping apparatus is well known to pump liquids, for example oil from a well to the surface through a string of tubing. The apparatus includes a string of sucker rods connected one to the other in end to end relation and the rod is located within the tubing. The bottom end of the lowermost sucker rod is connected to the plunger of any suitable pump. There is a valve arrangement that includes a standing valve and a travelling valve spaced apart from one another that permit the upward flow of liquid through the tubing as the pump plunger is raised and lowered by up and down movement of the string of sucker rods. All this is well known in the art and by way of example reference may be had to the teachings of Canadian patent 819,448 issued Aug. 5, 1969 to Donald E. Sable; U.S. Pat. Nos. 2,997,106 and 3,058,524 issued to Tripplehorn and U.S. Pat. Nos. 4,997,039 and 4,575,163 issued to Donald E. Sable. These patents address different problems in the pumping of oil from a well and disclose the use of fixed and movable scrapers to remove paraffin and other sediments which accumulate on the sucker rods and internal surface of the conduit during pumping of oil from a well. In that the subject is well covered in the foregoing documents there is no need to repeat the same herein and the subject of the foregoing references is incorporated herein by reference thereto.
In a conventional oil well pumping apparatus each sucker rod may have alternately fixed and movable scrapers thereon. A movable scraper is located between two scrapers rigidly or fixedly mounted on the shank at selected spaced apart distances. The spacing of the fixed scrapers may be for example equal to substantially one half of the length of the stroke or distance of travel of the string of sucker rods or more. There may for example be three fixed scrapers and two movable scrapers on a twenty-five foot long sucker rod and the length of travel of the sucker rod string may be only six feet.
Each scraper is generally in the form of a tubular body made of a suitable durable material such as that known by the trade-mark "Nylon" or the like for the movable scraper and a material known by the trade-mark "Ryton" for the fixed scrapers. Each scraper has an internal bore and external diameter correlated to the diameter of the sucker rod and internal diameter of the tubing in which it is employed. Each scraper has a fluted outer surface provided by spaced apart ribs that provide outer scraping edges and fluid passage channels therebetween. The spaced apart ribs, defining the channels therebetween, are at a selected angle to the longitudinal axis of the sucker rod. During pumping the angularly inclined fluid flow channels cause rotational movement of the movable scrapers as a result of relative movement of the liquid and the scrapers. The pitch or angular inclination of the ribs may be chosen as may be desired to provide the desired mechanical strength of the scraper and to permit a relatively low resistance to the flow of well fluids past the scraper and the desired rotation.
The movable scrapers, also sometimes referred to as ambulatory scrapers or migratory scrapers, each reciprocate back and forth between a pair of spaced apart scrapers fixed to the rod. A pair of fixed scrapers provide abutments for the movable scraper confining the same to assigned lengths of the sucker rod. The abutting surfaces normally lie in planes disposed normal to the axis of the sucker rod.
The movable scrapers rotate about the axis of the sucker rod on which they are mounted when there is relative movement between the movable scraper and the fluid. This rotation or spinning of the movable scraper occurs on each of the up and down stroke of the sucker rod. The upper end of the movable scraper will at one time abut against the bottom end of one fixed scraper and at another time the lower end of the movable scraper will abut against the upper end of another fixed scraper spaced from said one fixed scraper. The relative rotation of the fixed and movable scraper causes the abutting surfaces to wear. This wear can be rapid when abrasives are trapped between the abutting surfaces and which abrasives are normally present in the form of particulate sand particles in the oil being pumped. The sand is very abrasive and quickly wears out the abutting surfaces. Rotation of the movable scraper at the same time as wearing the abutting surface on the fixed scraper also causes wear on the sucker rod.
Replacement of the movable scrapers on a sucker rod is relatively simple because the sucker rod is merely forced through a longitudinal gap in the scraper. Replacement of fixed scrapers, however, is not as simple because they are normally molded onto the sucker rod.
It is known to have movable scrapers wherein the internal bore is flared to receive therein the outwardly flared part of an upset end portion of the sucker rod or alternatively a tapered shank portion projecting from a fixed scraper as the case may be. In this arrangement there are planar ends on the fixed and movable scrapers, but the area of such planar ends is reduced and thus wear more quickly. It is conceivable the planar ends could wear sufficiently as to cause the tapered end on the fixed scraper to tightly engage and become wedged in the tapered end recess portion of the movable scraper. This possibility would result in the movable scraper being fixed to the fixed scraper. This would increase the resistance for a reciprocal movement of the sucker rod string and also substantially reduce the intended cleaning action of the movable scraper. Also it is conceivable that extensive wear to the planar abutting surfaces could result in the tapered portion on the sucker rod projecting sufficiently into the movable scraper so as to cause the same to expand increasing the diameter to the extent that it could become wedged in the well tubing.
A principal object of the present invention is to provide means to prevent rotational movement of the movable scraper relative to the sucker rod prior to engagement of the abutment end surfaces of the movable and fixed scraper.